1. Field of the Invention
This invention relates to an adjustable valve system for an engine having an axially shiftable camshaft acting upon either valve lifters or rocker arms having pivoting rubbing block structures which accommodate changes in the cam lobe profile by pivoting about axes which are perpendicular to the axis of the camshaft, while being constrained by a spline and keyway structure from rotating about an axis parallel to the camshaft.
2. Disclosure Information
Internal combustion engine designers have considered the use of axially shifting camshafts for several years. Such camshafts use lobes characterized by a profile which changes with the axial position of the lobe. Thus, by positioning the camshaft in a desired axial location, the valve lift, valve opening duration, and other operating characteristics of the cam may be set according to the requirements of the engine.
U.S. Pat. No. 4,517,936 to Burgio di Aragona, U.S. Pat. No. 4,570,581, U.S. Pat. No. 4,693,214, and U.S. Pat. No. 4,773,359, all Titolo, all disclose a tappet for use of axially displaceable camshafts. The tappet uses a flat shoe for contacting a cam, with the shoe riding in an elongate bearing saddle. This system is quite bulky and uses a multitude of parts. Further, the system of the '936 patent would appear to be inoperative because no structure is shown for preventing displacement of the shoe due to the lateral thrust imposed by the cam lobe upon the lifter. Although the later patents in the series to appear to solve this difficulty, they never let it suffer from the problem of being an extensive size and therefore of an undesirable nature for compact engine construction.
U.S. Pat. No. 3,915,129 to Rust et al. discloses a cam follower having a ball with a flat surface for engaging the cam surface. This design does suffer from the disability that if the ball should leave the surface of the cam lobe, and such is frequently the case during high speed operation of an engine, the ball may very well rotate so that the flat spot is no longer in contact with the camshaft lobe. If such were to occur, rapid wear would quickly destroy the camshaft and the cam follower.
U.S. Pat. No. 1,500,556 to Goodwin discloses a cam follower having a rocker which is pinned to the cam follower and is not suitable for use in following a contoured axially shiftable camshaft.
U.S. Pat. No. 4,393,820 to Maki et al. and U.S. Pat. No. 4,850,311 to General Motors disclose a cardanic rocker arm and lifter assembly, respectively. These devices use non-rubbing type rotation to accommodate the relative movement needed between a rocker arm and mounting fulcrum and bucket type tappet, respectively. Neither of these patents disclose the anti-rotation features of a valve system according to the present invention.
It is an advantage of a system according to the present invention that a valve lifter made according to this invention will be physically compact and suitable for use with camshaft rubbing blocks which may be either flat or arcuate or which may include a roller assembly.
It is yet another advantage of the present invention that an adjustable valve system according to this invention may accommodate the use of camshafts having more aggressive profiles than the camshafts suited for use with known axially adjustable cam follower assemblies.
Other objects, features and advantages of the present invention will become apparent to the reader of the specification.